Exhaust systems are widely known and used with combustion engines. Typically, an exhaust system includes exhaust tubes or pipes that convey hot exhaust gases from the engine to other exhaust system components, such as mufflers, resonators, etc.
Most exhaust systems include diesel particulate filters (DPF) or NOx-storing catalysts. These filters or catalysts must be regenerated in regular intervals, as otherwise their flow resistance will increase excessively or their efficiency will decrease. Regeneration is referred to as “burning-off” because a thermal reaction takes place during the regeneration. This reaction can be initiated by a fuel or some other suitable, oxidizable fluid that can be directly introduced into the exhaust system upstream of the filter or catalyst.
In one known configuration utilizing a selective catalytic reduction (SCR) catalyst, the exhaust system includes an injection system with a doser that injects a reducing agent, such as a solution of urea and water for example, upstream of the SCR catalyst. The doser is typically mounted to a tube that connects the SCR catalyst to an upstream exhaust component. The doser typically sprays the urea directly into the exhaust stream immediately upstream of an inlet into the SCR catalyst. One disadvantage with this configuration is that the reducing agent may not be thoroughly mixed with the exhaust gas prior to entering the SCR catalyst.